The present invention relates to an image pickup device, and more particularly to an image pickup device which is capable of producing an excellent image if an image is picked up in a fluctuating state.
In recent days, as the users of an image pickup device become more and more, unskilled persons may more often handle the image pickup device, in addition, the image pickup device is likely to raise its zooming magnification.
It is likely that the unskilled persons, however, cannot firmly keep the image pickup device with their hands when they use it for picking up an image. And, even skilled persons may not firmly keep the image pickup device if they use the device with a high zooming magnification. The resulting images may be so vibrated that they become obscure. Moreover, when a user picks up an image on a moving place such as a car, the resulting images also may be often so vibrated that they become obscure.
There has been required an image pickup device which is capable of producing an excellent image when the device is handled in a fluctuating state.
Under those circumstances, there have been heretofore developed techniques for stabilizing a fluctuated image. One of such stabilizing techniques will be discussed below.
One of the conventional stabilizing techniques has been proposed in the JP-A61-198879. FIG. 1 is a block diagram showing an image pickup device employing the technique for correcting the fluctuated image. FIG. 2 is a schematic illustration for describing the operation of the image pickup device to which the technique is applied.
As shown in FIG. 1, 1 is an image pickup means, 2 is a motion vector detector, 3 is a field memory, and 4 is a readout position control means. As shown in FIG. 2, 5 is an image represented by a video signal sent from the image pickup means 1, 6 and 6' are screens displaying images of the current field and the previous one read out from the field memory 3, 7 and 7' are images of the current and previous fields displayed on the screens, and 8 is a motion vector. The following description is directed to the operation of the image pickup device employing the fluctuated image stabilizing technique as designed above.
At first, the image pickup means 1 outputs a video signal. The screen 5 represented by the video signal is shown in FIG. 2. The field memory 3 stores a one-field portion of the video signal. The motion vector detector 2 serves to detect parallel movement (referred to as a motion vector) of an image in the current field against the image in the previous field on screen out of the video signal. The motion vector is indicated by 8 in FIG. 2. The readout position control means serves to shift the position at which the video signal is read out of the field memory 3 of stabilizing the motion, based on the motion vector detector from the motion vector detector 2, such that the position is shifted from numerals 7 to 7' shown in FIG. 2.
If, therefore, the image pickup device handled in a fluctuating state results in producing fluctuated images indicated by 7 and 7' in FIG. 2, the movement of the images 7 to 7' can be relatively stabilized against the screens 6 and 6' represented by a video signal read out by the field memory 3. The stabilization provides an image formed as if the image pickup device were not fluctuated.
The foregoing image pickup device, however, can stabilize the fluctuation field-by-field but cannot stabilize a blurred image resulting from in-field fluctuation of the device. Hence, though the position of an image on screen is not moved, the blurring generated on edge portions of the image is varied, resulting in often generating a visually unnatural image.
FIG. 3 shows graphs for describing the foregoing disadvantage. FIG. 3a is a graph indicating how a point placed on an optical image is moved if an image is picked up in a fluctuating state. FIG. 3b is a graph indicating how a point on the image at each field matching to the point movement shown in FIG. 3a is changed. FIG. 3`c is a graph indicating fluctuation-stabilized images. As shown in FIG. 3a, if the image pickup device handled in a fluctuating state results in moving a point on the image, the point on the image at each field is moved between two fields 24 and it is blurred within each field itself in proportion to the speed of a point movement 22. (Hereinafter, the between-field movement 24 of the image is referred to as fluctuation and the in-field image blurring 22 is referred to as a blurring.)
If the image is fluctuation-stabilized, as shown in FIG. 3c, the point on the image stays on its position but is subject to the blurring 22 in proportion to the fluctuating speed of the image pickup device.
As shown in FIG. 3b, if the blurring 22 caused on an image at each field has the visually same direction as the between-field movement 24 of an image, the image is recognized as a natural motion picture. As shown in FIG. 3c, if the blurring 22 is caused to change in proportion to the speed at which the image pickup device is fluctuated, the image is recognized as a quite unnatural image even if the between-field movement of the image is stabilized and the image remains motionless.
As has been mentioned above, the image pickup device employing the conventional fluctuation-stabilizing technique causes a blurring mismatched to the between-field movement even on the stabilized image, resulting in producing a quite unnatural and unappreciable image from a visual point of view.